Ultracold quantum dynamics: Spin-polarized K+K₂ collisions with three identical bosons or fermions

We have developed a potential-energy surface for spin-polarized K(²S)+K₂(³Σ_u⁺) collisions and carried out quantum dynamical calculations of vibrational quenching at low and ultralow collision energies for both bosons ³⁹K and ⁴¹K and fermions ⁴⁰K. At collision energies above about 0.1 mK the quenching rates are well described by a classical Langevin model, but at lower energies a fully quantal treatment is essential. We find that for the low initial vibrational state considered here (v=1), the ultracold quenching rates are not substantially suppressed for fermionic atoms. For both bosons and fermions, vibrational quenching is much faster than elastic scattering in the ultralow-temperature regime. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states.